The analysis of engine oil or other lubricant for the purpose of identifying premature component wearing has been performed for several decades using optical atomic spectroscopy (e.g., atomic emission spectroscopy (AES), as well as its predecessor that has been in use as a field monitoring method, atomic absorption spectroscopy (AAS)). This technology has been the basis for the military aviation's Spectroscopic Oil Analysis Program (SOAP). However, this technology can sometimes lack of repeatability among different equipment and does not consider particles greater than 5 μm in diameter. Furthermore, SOAP typically uses optical atomic spectroscopy, which is an elemental analysis of the total oil sample and typically does not characterize individual particles in the sample.
Rotrode Filter Spectroscopy has been introduced in 1980 and it was commercialized by Spectro Incorporated (Littleton, Mass.). The method focuses mainly on the analysis of large particles in the oil and has proven to be effective to establish the source of wear material in a system already generating wear material [1].
Scanning electron microscope (SEM) equipped to perform X-ray spectroscopy has been used to characterize individual particles [2] for wear mode indicators. However, SEM has been considered to be unsuitable for routine monitoring of machine condition, for example as reported in Whitlock [3].